Herring Gull H-131304 1cy (argenteus), August 15 2003, Westkapelle, the Netherlands (51.33N - 03.25E).

This juvenile Herring Gull was ringed Bruxelles H-131304. Ringed as pullus on July 16 2003 at Zeebrugge, Belgium (51.20N 03.11E) It has slight wear in scapulars and wing-coverts, and some upper scapulars have been replaced. The gap in the upper lower scapular row is obvious when viewed from behind. 

In juvenile plumage, the head and under-parts are streaked grey-brown, rather pale on forehead and throat and with dark ear-coverts. The mantle and scapulars are brown based with buffish-yellowish fringes when the feathers are fresh. The notched pattern is repeated on the lesser, lower lesser and median coverts, although the medians have paler centres. The greater coverts show a 'piano-key' pattern; on the outer greater coverts as well. The tertials have an obvious notched pale fringe and transversal bar. The secondaries, primaries and primary coverts are dark with a small white tip, but the inner primaries show an obvious pale window, prominent from below and above. The under-wing is rather uniform grey-brown patterned. The tail has a broad sub-terminal band and isolated dark bars on the basal half. The iris is dark, the bill is blackish, sometimes with a paler base, and the legs are flesh-pink.
The partial autumn moult (moult into so-called "first winter" plumage) includes the body and head feathers. This moult starts as soon as the nest is abandoned (late June) and continues until January. In general, the head turns paler on throat and forehead. The breast will turn paler as well. The feathers on belly and vent will still be juvenile in most 1cy argenteus by November. From July onwards, the mantle and upper scapulars are moulted to second generation feathers, showing an anchor pattern and a dark base. The lowest row of scapulars are still juvenile by March in most 2cy birds (contra e.g. michahellis). The juvenile wing-coverts, rectrices and remiges start to bleach and show wear in the fringes from September onwards.